Currently there are at least two techniques for dredging or excavating sand or other mineral deposits. The first of these techniques involves onshore removal of the mineral using an excavator which then loads a truck. The truck transports the mineral for dumping or processing elsewhere. For example, some mineral sands in Western Australia are currently mined using this technique and then trucked to a processing plant for concentration of titaniferous ores contained within the mineral deposit. Some of the drawbacks with this technique include: the relatively high transportation costs; the fact that trucks require expensive pavement surfaces under their wheels; problems with dust control; and expense associated with road maintenance. Furthermore, trucks have often to take a long route around obstacles, and the tipped load from the trucks then has to be handled to its end use.
Dredges have also been widely used for the removal of sand or other mineral deposits from locations where water exists in abundance. Generally, the dredge is mounted on or as a barge which is then located in water at the site of the mineral deposit. The dredge progressively excavates mineral from the beach or other mineral deposit by slewing a rotating cutter head from side to side across a face of the deposit. The cutter head excavates the mineral and a slurry pump sucks up the mineral and pumps it via a pipeline to another location, such as a mineral sand concentrating plant. However, a relatively large volume of water is transported with the mineral deposit using the slurry pump. In locations where water is scarce, the water must be recycled to a dredge pit.
The volume of water retained with the mineral cannot be accurately controlled by dredging and inevitably excessive water is often pumped with the mineral. Thus, a relatively large amount of energy is expended pumping water rather than mineral. Although a certain amount of water is required together with the mineral to provide a pumpable slurry, this ratio often cannot be accurately controlled when dredging. Consequently, pumping costs are relatively high and, particularly where the slurry is to be pumped a long distance, may be prohibitive.